How can I microwave a "baked" potato so it doesn't tast, feel like cardboard?
Use a low(er) power setting.
A lot of people use the microwave to start a potato. About 2-3 mins, then some oil and salt and finish in 375oven for 20-30 mins.
On the few occasions that I microwave a potato, I also bake it for about 20 minutes afterward at a relatively high heat so that the skin crispens up.
I would use a real oven. I moved the nuker into the garage 12 years ago and don't miss it. While waiting for the potato to bake nicely in the oven (rubbed with olive oil and sea salt) enjoy a glass of chianti !